The present invention relates to a semiconductor device having a lateral bipolar transistor and a method of manufacturing the same.
In general, a bipolar transistor which is formed on an Si substrate or an SOI (Silicon On Insulator) substrate is formed in such a way as to have the vertical structure. Since the formation of the bipolar transistor in the vertical structure enables the base width to be thinned and also enables the junction area between an emitter and a base to be restricted roughly to the size of the active region, the high performance can be realized.
However, in order that the bipolar transistor may be formed in such a way as to have the vertical structure, an n+ type buried layer becomes essential thereto. On the contrary, in the case where the SOI substrate is employed in order to obtain the n type buried layer, an Si layer in the region in which a device is intended to be formed is compelled to become thick. Then, while there have been made a plurality of proposals for forming a lateral bipolar transistor on the SOI substrate having a thin Si layer, the process thereof is complicated.
For example, in IEDM (IEDM 93, pp. 75 to 78) 1993, there is proposed a bipolar transistor which is formed in such a way that an N type collector drift region is determined on the basis of an oxide film mask; n type impurity ions having a high concentration are implanted to form a collector electrode; then, p type impurity ions are implanted to form a base region; then, the base region is subjected to the silicon etching with the oxide film, with which the collector drift region is defined, as a mask to form a narrow base region; then, n type polysilicon is deposited to form an emitter electrode. In addition thereto, a lateral bipolar transistor which is formed on an SOI substrate is also reported in IEDM 91, pp. 663 to 667.
However, in the structure in which the lateral bipolar transistor is conventionally formed on the SOI substrate, the manufacturing process is compelled to be complicated.
In the light of the foregoing, it is therefore one object of the present invention to provide a semiconductor device in which a lateral bipolar transistor which is a match in the device performance for a vertical bipolar transistor can be formed through a simple manufacturing process, and a method of manufacturing the same.
According to one aspect of the present invention, there is provided a semiconductor device, wherein an electrode which is formed by filling a trench reaching a buried oxide film in an SOI substrate with an electrically conductive film or a metallic film is utilized as an emitter electrode and/or a collector electrode to simplify the manufacturing process and to form a lateral bipolar transistor which is a match in the device performance for a vertical bipolar transistor.
P type impurity ions for example are implanted through the trench by utilizing the vapor phase diffusion method, the plasma doping method, the oblique ion implantation method or the like, whereby it is possible to form a very thin base layer which has the vertically uniform concentration distribution ranging from the surface of the SOI substrate to the buried oxide film. In addition, for the formation of an emitter laver, there may also be adopted the method wherein after the trench has been filled with n type polysilicon for example, the overall substrate is exposed to the high temperatures to diffuse n type impurities from n type polysilicon. In addition, there may also be adopted the method wherein by the phosphorus deposition method is utilized which is employed for a long time as the method of after having formed a base layer, carrying out doping with phosphorus or the like, after having formed an emitter region, a metallic film is filled therein.
In addition, for the formation of an emitter electrode and a collector electrode of the bipolar transistor, there is adopted the structure in which the trench is filled with an electrically conductive semiconductor film or metal, whereby a voltage can be applied which is vertically uniform from the surface of the substrate to the buried oxide film, which leads to the enhancement of the performance of the lateral bipolar transistor.
In addition, according to another aspect of the present invention, after having formed an interlayer insulating film, an emitter electrode and/or a collector electrode of the bipolar transistor are/is formed. As a result, since the above-mentioned processing does not exert an influence on the fine patterning of MOS transistors which are formed together with the lateral bipolar transistors on the SOI substrate, it is possible to form the lateral bipolar transistors together with the fine MOS transistors on the SOI substrate. Furthermore, the above-mentioned processing is carried out after the formation of the interlayer insulating film, whereby a metallic film can be employed for the emitter electrode and/or the collector electrode.